The present invention relates to electric motor systems and more particularly to heat transfer methods in electric motor systems.
In a large number of electric motor applications, it is desirable to minimize heat retained in an electric motor. Maximum temperature rise specifications are prescribed for many applications by government and private regulatory agencies. Agencies such as Underwriters Laboratories specify maximum temperature rise limits for product applications as a requirement for agency listing or recognition of a product. Many consumer product manufacturers will not purchase components or products that are not listed or recognized by specific agencies, particularly Underwriters Laboratories. Therefore, the market viability of many products depends on the produces compliance with Underwriters Laboratory requirements.
It is known that smaller electric motors typically run hotter than larger motors in specific applications. Accordingly, it is known to provide a larger motor or a motor having a higher performance where applications using a smaller motor or a motor having lower performance fails to comply with heat rise specifications. For example, in the medical equipment industry, it is known that certain small motors have been heretofore unsuitable for use in hospital type beds and assisted chairs because the small motors fail to meet relatively low, for example 100xc2x0 C., Underwriters Laboratory heat rise requirement it is known to employ larger or higher performance motors that run cooler in such applications in order to meet the Underwriters Laboratory temperature rise requirement Such larger or higher performance motors are typically more expensive than smaller or lower performance motors.
It is known to provide heat sink components to radiate excess heat generated by many electronic and mechanical devices. Such heat sink components typically comprise a large surface area that is mounted directly against a surface area of a device to maximize heat transfer from the device to the heat sink. It is common practice in the electronic industry to provide a compliant gap filling substance between heat sink components and the device to which the heat sink is mounted to further promote heat transfer away form the device.
Accordingly, it is a primary advantage of the present invention to provide an improved method of heat transfer in electric motors by employing a thermally conductive gap filler between a motor windings end surface and a matin surface of a gear case. The method of the invention allows improved heat transfer away from the motor coils and allows a gear case to function as a heat sink.
An additional heat sink which may be mounted to an opposite end of a motor similarly using a thermally conductive gap filler between the heat sink and the motor windings surface provides additional heat transfer away from the motor. Additional heat transfer can be accomplished through the addition of a conductive gap filler. A conductive gap filler xe2x80x9cliquid form heat transfer compoundxe2x80x9d is placed into the gap between the motor and the motor lamination stack.
The heat transfer method of the present invention provides sufficient additional cooling to an electric motor so that a small or low performance inexpensive motor complies with the Underwriters Laboratory heat rise specification for use in hospital type beds and assisted chairs.
It is to be understood that various changes can be made by one skilled in the art in one or more of the several parts of the invention described herein without departing from the scope of the invention.